Control system for water heaters



July 23, 1968 P. DIETIKER CONTROL SYSTEM FOR WATER HEATERS Filed Aug. 22, 1966 TRANSISTOR PILOT BURNER HEATED THERMOPILE ROD AND TUBE VALVE ACTUATOR MAIN BURNER SUPPLY PIPE INVENTOR. PAUL DIETIKER ATTORNEY.

United States Patent "O 3,393,671 CONTROL SYSTEM FOR WATER HEATERS Paul Dietiker, Redondo Beach, Calif., assignor to Honeywell Inc., Minneapolis, Minn., a corporation of Delaware I Filed Aug. 22, 1966, Ser. No. 573,995 2 Claims. (Cl. 126351) ABSTRACT OF THE DISCLOSURE A control system for an anode-protected, gas water heater, wherein a thermopile heated by a pilot burner is in series with an anode projecting into a tank of water and the emitter-base control circuit of a transistor, and a coil of a gas safety valve is in series with the thermopile and the emitter-collector output circuit of the transistor, so that only if the anode is functioning properly, to prevent electrolytic deterioration of the tank, will the safety valve be held open.

This invention relates to a transistor control circuit and, more particularly, to a control system for a hot water heater having an anode and a combined electric safety and thermostatic gas flow controller for the heater wherein a transistor control circuit is used for controlling electric current flow to both the anode and the controller.

Water heater installations making use of an anode for conducting low voltage and low amperage current between the anode and the walls of the water heater, which is heated by a "burner having controls that are also energized by the same voltage supplied to the anode, are well known in the art, as disclosed in Andrus Patent No. 2,748,250. This invention is directed to an improved control circuit for a water heater anode and a gas flow control means, by controlling these elements through a transistor circuit in a manner which provides safe operation of the water heater as well as safety shutdown thereof in the event of pilot flame failure or deterioration of the anode to the extent that a high resistance is built up between the anode and the metallic water tank so that the cathodic protection ceases to function. It is to be noted that .in all of the Andrus patent systems except the one of FIGURE 2, the ceasing of the cathodic protection, as by an open circuit or high resistance increase, would not cause safety shutdown of the fuel supply so, in that respect, the invention to be presently described, besides providing all of the control functions of the Andrus systems, is an improvement thereover. As to the system of FIG- URE 2 of Andrus, it is very unreliable as to the electric power unit circuit as that units external circuit would have to have a much greater resistance than that of the variable 50 ohms to 2000 ohms of the anode-probably 50 ohms total for stable balancing of the circuit for a reasonable period of deterioration of the anode. Such a system would require too high a potential to be developed 'by a practical size of thermopile, approximately to volts. The thermopile used in this invention generates from 1.7 to 2.0 volts.

The single figure of the drawing is a fragmentary showing of a water heater of the above-mentioned type as well as a schematic showing of the control apparatus and circuit thereof.

Reference numeral 1 designates a metallic water heater tank in which a conventional metallic anode 2 is suitably mounted in an aperture 3 in the tank, preferably in the center of the top wall thereof. The water tank may also be of the type having a glass lining. The anode which may vary in resistance between 50 and 2000 ohms, with the resistance through the water included, extends through an insulator 4 which in turn is mounted on a mounting 3,393,671 Patented July 23, 1968 plate 5, suitably secured to the water tank. A conventional manifold valve 6 is screw threaded into a threaded aperture 7 in the lower side wall of the water tank and has a rod 8 and tube 9 Water temperature sensing unit projecting into the tank. The thermostatic unit is adapted to operate a gas valve (not shown) within the manifold valve body and is in series with a safety valve 10 that is adapted to be held open by means of a conventional thermopile energized'power unit 11. A gas supply pipe 12 is connected to the manifold valve while a pipe 12a connects an outlet of the manifold valve to a main burner (not shown) for heating the water heater. A pilot gas supply pipe 13 leads from the manifold valve, downstream of the safety valve 10, to a pilot burner (not shown). The pilot burner is adapted to heat a thermopile generally designated by the reference numeral 14.

One side of the thermopile is connected by a lead or conductor 15 to the mounting plate 5 of theanode and through a separate conductor 16 to one side of a coil (not shown) of the power unit 11. The other side of the thermopile is connected by a conductor 17 to the emitter electrode 18 of a transistor 19 and through a separate conductor 20 to one end of a resistor 21. The base electrode 22 of the transistor is connected to the other end of the resistor 21 and through a conductor 23 to the terminal 2a of the anode 2. The collector electrode 24 of the transistor is connected through a conductor 25 to the other end of the coil of the power unit.

It is thus seen that current will flow from the thermopile 14, when heated by a flame at the pilot burner, through the emitter and base of the transistor and through a parallel circuit therewith through resistor 21 to the anode 2 and from the anode through the water in the water heater to the water heater tank and back to lead 15 connected to the other side of the thermopile. When the potential buildup across the emitter and base has reached a preselected amount, the current from the thermopile will also flow through the collector 24 and through the lead 25, power unit coil, and lead 16 to the lead 15 and the other side of the thermopile. As long as there is a flame present at the pilot burner to energize the thermopile, the safety valve 10 will be held open in a conventional manner and a protective current flow will fiow between the anode and the water tank, to prevent deterioration of the water tank in the manner taught by the prior art, as illustrated in the Andrus patent. Also, as long as there is an adequate anode 2 present as to keep the resistance of the control circuit through the emitter 18 and base 22 sufliciently low, as to render the control circuit of the transistor conductive, the current to the magnet will remain sufficient to keep the magnet energized. The resistor 21 is sufficient to keep the current low so that the power unit current will not drop below the drop-out value. However, if the pilot flame should go out or the anode deteriorate too much, the safety valve will close. The home owner will become aware of this shutdown condition by the lack of hot water in the water system.

From the above description of the preferred embodiment of the invention, it is obvious that the invention is an improvement over the prior art and that slight modifications may be made in the system as illustrated without departing from the spirit of the invention. Therefore, the scope of the invention should be determined from the appended claims.

I claim as my invention:

1. In a control system for a water heater having a conventional size anode extending into a metallic water tank and a main gas burner for heating the tank, the combination comprising a thermostatic gas valve having a water temperature sensing means constructed for mounting on said tank and a low voltage, electric safety valve having 3 4' first and second terminals and being in gas flow series balanced electrically that only if a predetermined current with said thermostatic valve. for controlling gas flow to r flow existsbetween the anode a n d tank will thetransisto said main burner; a thermoelectric generator having first be conductive of current to the safety valve. and second terminals and being constructed for mounting 2. A control system as defined in claim 1 wherein said adjacent said main burner and having a pilot burner for 5 thermoelectric generator is one that develops a maximum heating said thermoelectric generator and for igniting said of two volts.

main burner; a transistor having an emitter electrically R ted connected to the first terrnlnal of said generator, a base eferences Cl electrically connected to said anode and a collector con- UNITED STATES PATENTS nected to the first terminal of said safety valve; a resistor 10 2,748,250 5 /1956. Andrus electrically connected across said emitter and base; the 2,879 353 3/1959 Hilgeft 126-351 second terminal of said generator being electrically con- 3,050,933 8/1962, Fokker,

nected to said second terminal of said safety valve; and means for electrically connecting said second terminal of JAMES W. WESTHAVER, Primary Examiner. said generator to the water tank; the system being so 

